The Hog Louse 717 



nations rospectively of the transverse conjunctivae between the pro- and 

 the mesothorax and between the pro- and the mesosternum. 



A second structure hitherto undescribcd in the Siphunculata is found 

 in the head, under the posterior lobes of the brain. The position and 

 structure of this pair of bilaterally symmetrical circular bodies suggests 

 their interpretation as the " corpora allata " of Heymons and other 

 investigators (cited iDy Bcrlese, 1909:588, and by Schroder, 1912-13:86). 



In the study of the stomodaeum and the mouth parts, the aim has been 

 to present as accurate a picture as possible of their anatomical structure, 

 musculature, and working. Their homology is not touched upon, l^ecause 

 in the case of structures so far modified from the generalized type, inter- 

 pretation should rest upon an investigation begun with the earliest 

 appearance of segmentation in the embryo and continued to maturity. 

 Cholodkovsky (1903:120) alone has touched upon this aspect, in his 

 work on the man-infesting pediculi, whose pharynx and mouth parts are 

 similar in plan to those of the hog louse. In none of the sections of the 

 alimentary canal have protozoan parasites been found, and the physiology 

 of digestion has been touched upon but briefly. 



The reproductive systems and the secondary sexual characters resem))le 

 those of other members of the order, but in the female no receptaculum 

 entering the uterus has been found. According to Harrison (1916 b: 221), 

 " in the Ischnocera, and in all Anoplura save Pediculus, a receptaculum 

 of remarkable structure opens into this uterus by a long narrow duct, 

 the entry of the duct into the receptaculum being marked by a conspicuous 

 chitinous ring." 



The experimental work on the JDiology of the species has been carried 

 out with much care. In the acceptance of the resulting figures indicating 

 periods in the life history, however, it must be born(; in mizid that in the 

 natural habitat, with continual opportunity of feeding, these periods 

 may be somewhat shorter. 



ACKNOWLEDGMENTS 



Thanks are due to Dr. V. A. Moore, of the New York State Veterinary 

 ■ College at Cornell University, for facilities for keeping a hog for experi- 

 mental work; to the Department of Entomology of the New York State 

 College of Agriculture at Cornell University, for the payment of the 

 expenses connected with keeping the hog; to the Depai'tment of Animal 



